The present invention relates to a method for ultra-fine particle separation, such as for purification and recovery of clays for use as rheological control agents and for use in the preparation of nanocomposites. More particularly, the invention relates to an improved aqueous based pseudo-phasic extraction method for the simultaneous surface modification and purification of exfoliated clays.
There are numerous biphasic extraction methods currently known for the purification of clays which are intended for use as theological control agents in a wide range of water-based products including inks, paints, coatings, cosmetics, lubricants, greases, caulks, pharmaceuticals, fertilizers, pesticides, oil drilling muds, binders, and adhesives. In the area of ultra-fine particle separation, one method is an aqueous biphasic extraction (ABE) process which involves a heterogeneous liquid/liquid method wherein species partition between two immiscible aqueous phases. The extraction system is typically generated by combining an aqueous salt solution with an aqueous polymer solution. Example polymers that can be used are polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, and polypropylene glycol. An ABE method produces two distinct liquid layers that are immiscible, yet each liquid layer contains over 70% water. Some examples of inorganic salts that can be used to form ABE systems in combination with polymers such as polyethylene glycol include the sodium salts of carbonate, sulfate, phosphate, and hydroxide. The selective partitioning of particulates in ABE systems is based on complex physicochemical interactions between the particle surface and the liquid phases, rather than bulk phase properties like density. An ABE system can be operated in a continuous, counter-current fashion to achieve high levels of selective separation. The operating conditions for previous conventional ABE methods involve a strict two-phase regime in which the selective partitioning of ultrafine particulates occurs between the bulk liquid phases.
While biphasic separation processes are well developed, there still remain substantial problems in separating certain substances by this methodology. For example, silica-based minerals such as quartz, cristobalite, and opal are considered impurities in numerous common minerals, such as clays. Historically, efficient and inexpensive methods for the separation and recovery of phyllosilicates, kaolin and smectite clays in particular, from silica-based minerals (for example opal in smectite clays) has been unavailable. The issue in kaolin purification concerns the removal of smectites, cristobalite, and iron and titanium containing minerals. Current approaches used in the purification of clays, especially smectite clays, involve sequential treatment of an aqueous clay slurry in a number of unit operations including high shear dispersion, sodium exchange, and particle size separation. The latter series of unit operations may include screens, hydrocyclones, low-speed centrifuges, and high-speed centrifuges. Treatment approaches that include high-speed centrifugation, as exemplified by the use of a disc centrifuge, are highly energy intensive and expensive to maintain due to rapid abrasion of the processing equipment. In addition, these processes all suffer from an inability to separate mineral impurities from the clay in cases where the particle size distributions of the various mineral impurities overlap with that of the clay minerals. One example of a particularly difficult separation that has resisted traditional methods is the removal of opal from smectite clays, and another example is the removal of titanium dioxide from kaolins.
Furthermore, under prior art methods it has not been possible to make nanoscale particle/particle separations based on surface chemical characteristics. This ability is provided by the present invention and makes it possible to separate exfoliated clay platelets having a thickness of about 10 xc3x85 from platelets that remain stacked in naturally occurring booklets (i.e., stacks of individual clay crystals arranged like the pages in a book to form agglomerations of stacked, non-exfoliated clay particles). The homogeneous dispersion, on the nanoscale level, of the clay platelets throughout a composite matrix as individual platelets of about 10 xc3x85 thickness is regarded as a key characteristic of nanocomposites and distinguishes such materials from conventional plastic/mineral composites. Thus, the purified clays produced by this invention are particularly well suited for incorporation as nanocomposites since the process selectively recovers highly purified clays on the basis of surface chemical characteristics.
It is therefore an object of the invention to provide a novel article of manufacture and method of separating clay from clay impurities.
It is another object of the invention to provide a novel article of manufacture and method for separating a preferred mineral, element or chemical composition from a matrix including, without limitation, mineralogical compositions, rocks, soils, ores, mineral-containing waters and the like, whether processed or unprocessed.
It is still another object of the invention to provide a novel article of manufacture and method for recovering a preferred element, mineral or composition from an industrial waste, treated or untreated, including, without limitation, wastewater, solid waste, fly ash, byproducts of combustion, products of combustion residue and the like.
It is another object of the invention to provide an aqueous pseudophasic extraction method for separating clay from clay impurities.
It is a further object of the invention to provide a novel article of manufacture and phase separation method which produces very high surface chemical purity clay when applied to a clay feed.
It is still another object of the present invention to provide a novel article of manufacture and method for recovering exfoliated clays from clay/impurity mixtures.
It is another object of the present invention to provide a novel article of manufacture and method for preparing highly purified clays from clay/impurity mixtures at a reduced cost compared to current clay purification methods.
It is yet another object of the present invention to provide an improved article of manufacture and a particle/particle separation method which utilizes a pseudophasic system to selectively form a polymeric coating on particles of a mineral such as clay to enhance particle/particle separation.
It is yet an additional object of the invention to provide a novel article of manufacture and method for preparing highly purified clays which can be used to control the rheology of aqueous-based systems.
It is also another object of the invention to provide an improved article of manufacture and a method of aqueous-based, pseudo-biphasic extraction for separating and recovering clay from clay ores, soils, impure clays and the like.
It is another object of this invention to provide a novel article of manufacture and method for preparing highly purified clays which are incorporated into polymeric systems as nanocomposites.
It is another object of this invention to provide a novel method for preparing surface-treated clays for use in foods, pharmaceuticals, cosmetics, and fire retardants.
It is another object of this invention to provide highly purified clays for further treatment with existing technologies to produce organophillic clays.
Further objects and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention when taken into conjunction with the accompanying drawings.
In one form of the present invention, a purified clay is provided by the treatment of an ore or other material which contains a clay and one or more impurities. Impurities can be any material from any source except the desired clay product and can include mineral or chemical impurities from any source and unexfoliated clay particles. Other forms of the invention provide an article of manufacture and method for separating a preferred mineral, element or chemical compound from a matrix including, without limitation, mineralogical compositions, rocks, soils, ores, mineral-containing waters and the like, whether processed or unprocessed or for recovering a preferred element, mineral or other composition from an industrial waste, treated or untreated, and including, without limitation, wastewater, solid waste, fly ash, byproducts of combustion, products of combustion residue and the like.
In the case of clays being purified, the clay is preferably purified by dispersing a quantity of finely-divided raw clay feed in water along with a water-soluble polymer, such as polyethylene glycol, to form a pseudophase. The water-soluble polymer is preferably added in a sufficient amount to form a substantially monomolecular coating of the polymer on the basal surfaces of the clay. Excess amounts of the polymer can also be used in the process without detriment and can in some cases be beneficial. In some embodiments, an inorganic salt, preferably a monovalent metal salt, such as sodium carbonate, can be added to substitute sodium for exchangeable calcium or magnesium ions in the clay. Utilizing the salt also improves the performance of the extraction method and improves dispersion and exfoliation of the clay. Another polymer, such as polypropylene glycol, can also be added to the mixture to preferentially coat the surfaces of the impurity and form a pseudo-biphase. Mixing is typically carried out for about ten to sixty minutes at an elevated temperature in the range of about 40 to 70xc2x0 C. Under these mixing conditions, a polypropylene glycol phase, undergoes a density inversion and becomes more dense than water and is separated out leaving a substantially impurity free clay. Further, the two polymers are preferably added sequentially rather than simultaneously in order to enhance the effectiveness of the process.
The above described objects and embodiments are set forth in the following description and illustrated in the drawings described hereinbelow.